loki/docs/sources/get-started/hash-rings.md

---
menuTitle: Hash rings
title: Consistent hash rings
description: Describes how the Loki architecture uses consistent hash rings.
weight: 800
aliases:
    - ../fundamentals/architecture/rings
---
# Consistent hash rings

[Consistent hash rings](https://en.wikipedia.org/wiki/Consistent_hashing)
are incorporated into Loki cluster architectures to

- aid in the sharding of log lines
- implement high availability
- ease the horizontal scale up and scale down of clusters.
There is less of a performance hit for operations that must rebalance data.

Hash rings connect instances of a single type of component when

- there are a set of Loki instances in monolithic deployment mode
- there are multiple read components or multiple write components in
simple scalable deployment mode
- there are multiple instances of one type of component in microservices mode

Not all Loki components are connected by hash rings.
These components need to be connected into a hash ring:

- distributors
- ingesters
- query schedulers
- compactors
- rulers
- bloom compactors (Experimental)

These components can optionally be connected into a hash ring:
- index gateway


In an architecture that has three distributors and three ingesters defined,
the hash rings for these components connect the instances of same-type components.

![Distributor and ingester rings](../ring-overview.png "Distributor and ingester rings")

Each node in the ring represents an instance of a component.
Each node has a key-value store that holds communication information
for each of the nodes in that ring.
Nodes update the key-value store periodically to keep the contents consistent
across all nodes.
For each node, the key-value store holds:

- an ID of the component node
- component address, used by other nodes as a communication channel
- an indication of the component node's health

## Configuring rings

Define [ring configuration](https://grafana.com/docs/loki/<LOKI_VERSION>/configure/#common) within the `common.ring_config` block.

Use the default `memberlist` key-value store type unless there is
a compelling reason to use a different key-value store type.
`memberlist` uses a [gossip protocol](https://en.wikipedia.org/wiki/Gossip_protocol)
to propagate information to all the nodes
to guarantee the eventual consistency of the key-value store contents.

There are additional configuration options for distributor rings,
ingester rings, and ruler rings.
These options are for advanced, specialized use only.
These options are defined within the `distributor.ring` block for distributors,
the `ingester.lifecycler.ring` block for ingesters,
and the `ruler.ring` block for rulers.

## About the distributor ring

Distributors use the information in their key-value store
to keep a count of the quantity of distributors in the distributor ring.
The count further informs cluster limits.

## About the ingester ring

Ingester ring information in the key-value stores is used by distributors.
The information lets the distributors shard log lines,
determining which ingester or set of ingesters a distributor sends log lines to.

## About the query scheduler ring

Query schedulers use the information in their key-value store
for service discovery of the schedulers.
This allows queriers to connect to all available schedulers,
and it allows schedulers to connect to all available query frontends,
effectively creating a single queue that aids in balancing the query load.

## About the compactor ring

Compactors use the information in the key-value store to identify
a single compactor instance that will be responsible for compaction.
The compactor is only enabled on the responsible instance,
despite the compactor target being on multiple instances.

## About the ruler ring

The ruler ring is used to determine which rulers evaluate which rule groups.

## About the index gateway ring

The index gateway ring is used to determine which gateway is responsible for which tenant's indexes when queried by rulers or queriers.

## About the Bloom Compactor ring
{{% admonition type="warning" %}}
This feature is an [experimental feature](/docs/release-life-cycle/). Engineering and on-call support is not available.  No SLA is provided.  
{{% /admonition %}}

The Bloom Compactor ring is used to determine which subset of compactors own a given tenant, 
and which series fingerprint ranges each compactor owns. 
The ring is also used to determine which compactor owns retention. 
Retention will be applied by the compactor owning the smallest token in the ring.